Rhodium complexes bearing 2-(pyridin-2-yl)hydrazino acenaphthene-1-one: synthesis, structure and electrochemical studies

Abstract

Metal complexes based on mono(arylhydrazino)acenaphthenones (Ar-mhan) are extremely rare. In this work, synthetic routes for previously unknown rhodium complexes containing 2-(pyridin-2-yl)hydrazino acenaphthene-1-one (Py-mhan) are proposed. The interaction of RhCl₃·3H₂O with Py-mhan, depending on the conditions, led to two anionic complexes: (HPy-mhan)⁺[Rh(Py-mhan)Cl₃] (1) and (NBu₄)[Rh(Py-mhan)Cl₃] (2). The complexes were characterized using X-ray diffraction analysis, elemental analysis, and IR- and ¹H NMR-spectroscopies. The electrochemical properties of complex 2 were investigated using cyclic voltammetry. Complex 2 demonstrated irreversible reduction at −0.69 V (vs. Ag/AgCl), which is accompanied by the elimination of chloride ligands to give a Rh(I) complex namely [Rh(Py-mhan)(CH₃CN)] (3). Complex 3 was isolated by electroreduction of complex 2 on a carbon glass electrode and characterized by EDS analysis, CHN analysis, ¹H NMR spectroscopy and cyclic voltammetry. For complexes 2 and 3, reversible reduction processes localized on Py-mhan were found. To confirm the nature of electrochemical transformations for complexes 2 and 3 in solution, quantum chemical calculations were performed.